Tests for excitations and ground state modifications needed

I don't believe our multideterminant tests fully cover the common cases of addition or subtraction of an electron for EA/IP calculations. The multideterminant and configuration interaction tests largely cover the case of creating an exciton, but an explicit promotion test would not be amiss, particularly with splines. e.g. Using carbon diamond 1x1x1.

If we conclude that these cases are fully covered I will close the issue.

Review the existing multideterminant and configuration interaction tests, then identify how carbon diamond 1x1x1 is represented for EA/IP calculations. Check coverage for electron addition, subtraction, and explicit promotion, including spline cases. The work is done when the common ground-state modification and excitation cases are covered or existing coverage is confirmed sufficient.

Written by the indexing model from the issue text.